libpkgconf: parser: gracefully handle pkgconf_fgetline failures With the move to dynamic buffering of pkg-config files, it is possible for pkgconf_fgetline to leave the buffer in an unwritten state, where a buffer will not be allocated. We must gracefully handle this situation, so we bail early and re-enter the loop to try reading the buffer again. If it fails again, then we finish parsing the already read pkg-config data. Related: https://github.com/pkgconf/pkgconf/issues/384 Signed-off-by: Ariadne Conill <ariadne@ariadne.space>